Display apparatuses, such as television sets or monitors, may include On-Screen-Display (OSD) insert circuits for displaying an additional image, such as a state of the apparatuses, a screen for user's adjustment, or a teletext. The OSD insert circuits insert an additional image signal, such as the teletext or the menu, into a video signal displayed on the display apparatuses for user's adjustment. A conventional OSD insert circuit for inserting an analog additional image signal into an analog video signal is disclosed in Japanese Patent Laid-Open Publication No. 5-344438.
In the conventional OSD insert circuit, both of the video signal and the additional image signal are analog signals. The conventional OSD insert circuit can not handle a digital video signal. Thus, in a digitally-controlled display apparatus, such as a liquid crystal television set necessarily converts the digital video signal into an analog video signal, which is originally unnecessary for the digital video signal, inserts the additional image signal into the converted analog video signal, and converts it into a digital signal in order to insert the additional image signal. These operations raise a cost and provide performance degradation.